This invention relates generally to composite constructions of dissimilar polymers and more specifically to composites of polyvinylidene fluoride/polymethyl methacrylate alloy compositions with dissimilar thermoplastic polymers and to the method of making such constructions by two-layer coextrusion with recycling of scrap material produced in the process.
Polyvinylidene fluoride resin (PVDF) is a high-performance member of the fluorocarbon polymer class, combining excellent resistance to chemicals and weathering with ease of processing. It is, in many ways, a bridge between low-cost, general purpose polymers and higher-cost, ultra-high performance fluoropolymers. One of the outstanding physical properties of PVDF is its resistance to severe outdoor weathering conditions, which include ultraviolet radiation and harsh extremes of temperature and humidity. These properties make PVDF an attractive prospect as a protective cap stock material when laminated to less durable polymers, such as acrylonitrile-butadiene-styrene (ABS) and polyvinylchloride (PVC). A convenient method of forming such composites or laminates is by coextrusion. Although coextrusion processes involving dissimilar polymers to form composites are well-known, many are feasible only if an adhesive layer is employed to make a bond possible between incompatible materials. Generally, coextrusion without an adhesive layer is possible only with polymers possessing a high degree of compatibility, such as within a family or class of polymers. When dealing with the relatively inert fluoropolymers, such as PVDF, the obtaining of satisfactory adhesion between layers in a two-layer coextrusion process has been extremely difficult. One such process for forming laminates of PVDF and polyurethanes is disclosed in U.S. Pat. No. 4,221,757. The PVDF is selected to have certain viscosity properties in order to obtain adhesion. Another such process for forming laminates is disclosed in U.S. Pat. No. 3,968,196 where PVDF is laminated to polystyrene by the control of viscosity properties. In any such coextrusion process, scrap material is produced, for example, due to edge trimming of the product and during start-up when the correct processing conditions are being established to produce product which meets specifications. This scrap represents a loss because it cannot be recycled to the process by incorporation into the base resin due to the incompatibility of PVDF with the base resin which causes a deterioration in the properties of the composite. We have now found that composites of PVDF alloys with other thermoplastic polymers including acrylonitrile-butadiene-styrene terpolymer (ABS), polycarbonate (PC), PC/ABS alloys, polyvinylchloride, methylmethacrylate-acrylo-nitrile-butadiene-styrene (MABS), and other acrylic polymers can be prepared without need for an adhesive layer or the requirement for matching of viscosity properties, with the ability to recycle scrap composite material to the process.